Automatic rotor balancing apparatus



y 1949- Y H. M. ZENOR I I I 2,474,883

AUTOMATIC RO'IOR BALANCING APPARATUS Filed Sept.20, 1945 5 Sheets-Sheet 1 ELECTRONIC CMTMLLER 5 PEA D CMTROL REVE/VRSE y 1949 H, M. zENo| 2,474,883

AUTOMATIC ROTOR BALANCING APPARATUS Filed Sept. 20, 1945 5 Sheets-Sheet 2 INVENTOR (/6//$ M- ZENaR Filed Sept. 20, 1945 5 Shets-Sheet 5 July 5, 1949. H. M. ZENOR 2,474,883

AUTOMATIC ROTOR BALANCING APPARATUS July 5, 1949. H. M. ZENOR AUTOMATIC ROTOR BALANCING APPARATUS Filed Sept. 20, 1945 5 Sheets-Sheet 4 V A A Y Y -INVENTOR flugx/fis A7. ZENOR p EY I July 5, 1949. M. ZENOR i 3 I AUTOMATIC ROTOR BALANCING APPARATUS Filed Sept. 20, 1945 5 Sheets-Sheet 5 r/l. TEn flMPL.

INVENTOR f/uallzs M. Z ENOR Patented July 5, 1949 AUTOMATIC ROTORBALANCIN APPARATUS Hughes M. Zenor, Kittredge, Colon. assignor to The Sperry Jorporation, a corporation of Delaware Application September 20; 1945, Serial No. 817,507

7 Claims. '(Cl. 51-154) This invention relates generally to the balancing of rotors, and the invention has reference more particularly to automatic rotor balancing apparatus for automatically static-dynamically balancing gyroscope rotors, flywheels, etc., while the latter are actually rotating.

In Patent No. 2,243,45 there is disclosed a novel balancing apparatus wherein indication is given of an unbalanced condition and the location of such unbalance is indicated. The rotor is then removed from the machine and the material removed to bring about a balanced condition, the rotor then being re-inserted into the machine and again tested.

In the present machine the rotor is once inserted and stays in the machine, and the material is automatically removed from the rotor while the same is in the machine, until a balanced condition is reached. The principles 01' the present invention are also applicable to manually operated balancin machines as well as to automatic balancing.

The principal object of the present invention is to provide a novel automatic rotor balancing system wherein a rotor is inserted into the apparatus and is automatically tested for unbalance' and the material is removed automatically from the rotor to balance the same, whereupon the rotor automatically ceases its rotation and can be removed in a fully balanced condition.

Anothenobject of the present invention lies in the provision of novel balancing apparatus and method wherein means is provided for producing signal voltages proportional to the amount of unbalance at a, frequencypredetermlned by the rotor speed, means being provided for receiving such voltages and for determining whether to remove static or dynamic unbalance by reversing the polarity of at least a portion of the signal voltages, further means being provided for automatically removing material from the rotor at the proper position or positions to eliminate both static and dynamic unbalance thereof.

The invent on in another of its aspects relates to novel features of the instrumentalitles described herein for achieving the principal objects of the invention and to novel principles employed in those instrumentalites, whether or not these features and principles are used for the said principal objects or in the said field.

A, further object of the invention is to provide improved apparatus and instrumentalities em bodying novel features and principles, adapted for use in realizing the above objects and also adapted for use in other fields.

Other objects and advantages of this invention will become apparent as the description proceeds.

The terms "static unbalance" and "dynamic unbalance are used in this specification in the same sense as that defined by J. P. Den Hartogin his book on Mechanical Vibrations," pages 276 and 277.. Thus, static unbalance is that unbalance which can be removed by placing the shaft of the rotor to be balanced on parallel knife edges and removing and adding weights until there is no tendency for the rotor to turn, regardless of its angular position. Dynamic unbalance is defined as that unbalance which cannot be removed by a, static test The magnitude and angular position of the dynamic unbalance can be determined only by rotating the rotor.

In carryin out the method of this invention, metal is removed from any two predetermined planes, such as the upper and lower end surfaces of the rotor to be balanced, though any planes adapted to be operated upon by standard balancing machines are suitable. To correct for static out of balance, equal quantities of metal are removed from each of the selected planes and at the same angular displacement from any selected axis. Thus, as shown in Fig. 7, equal quantities of metal M; are removed from each of the planes and at thesame angular displacement 0. from the axes x at the top and bottom of the rotor extending at right angles to the rotor axes. .To correct for dynamic out of balance, equal quantities of metal Ma are removed from each of the planes, but at angular displacements differing by i. e. at diametrically opposite points, as shown in Fig. 7. Thus, the rotor is balanced dynamically and statically, or vice versa, by cutting metal in each case from both ends of the rotor.

} The underlying theory of balancing is based on the fact that, assuming a fixed rotor speed, the rotating deflection of the rotor shaft, rotor casing, etc., has a fixed phase relation to the disturbing force of weight, the deflection being apparent as vibration. The motion resulting at either end of the rotor from unbalance of the rotor is approximately circular in a plane perpendicular to the rotor shaft. Thus, a particle on an end of the rotor axis moves in a circular path and has a definite phase or angular relation to the unbalanced weight on the rotor so that should the unbalance of the rotor be advanced by a certain angle,the particle on the rotor axis will be correspondingly advanced by the same angle in its circular path.

a waees The movements of the particles on the two ends of the rotor axis do not necessarily have the same magnitude or angle. If the rotor is dynamically balanced and statically unbalanced, the particles on both ends of the rotor will move in the same 'circular pattern, with the same amplitude, and

with the same angle. If the rotor is statically balanced and dynamically unbalanced, the particles on both ends of the rotor axis will move in circular patterns of the same magnitude but 180 difference in angle. Thus. if pick-offs of equal sensitivity are placed on each end of the rotor on the aXis of rotation and their signals are added, the vibration from both ends due to static unbalance will be in phase, and the signal output will be twice that of each pick-oil. If the unbalance is dynamic, the signal vibration of the two pick-offs will be 180 out of phase, cancelling each other, and giving no signal. Therefore, for this condition, only the static unbalance is indicated, the signal being unaffected by the dynamic out of balance.

If the polarity of the voltage from one of the pick-offs is reversed (by interchanging the two leads to this pick-off) and their signals added, the total signal output will be zero for static unbalance, and twice the signal for each pick-oil for the dynamic unbalance. Thus, by switching the polarity of one of the pick-ofis, it is possible to determine the magnitude and the angle of both the static and the dynamic unbalance, which is sumcient information for the balancing of a rotor, making a convenient way of obtaining a signal for the automatic removal of metal for the automatic balancing of a rotor.

To correct for the static unbalance. equal amounts of metal will be removed from each of the balancing planes, from the same side of the rotor. To correct for the dynamic .unbalance, equal amounts of metal will be removed from each of the balancing planes on diametrically opposite sides of the rotor.

A more comprehensive understanding of this static-dynamic method of balancing will be obtained from the following mathematical analysis:

Referring to Fig. 8, it can be assumed that any unbalanced rigid rotor'can be balanced by removing metal at two positions on planes A and B suitably chosen. In the rigid rotor, of Fig. 8, the mass M1 is removed at angle 01 in plane A, and mass M: is removed at angle 02 in plane B. By proper choice of masses Ma and Ma and angles d and 0;, the same efl'ect can be obtained from the rotor.

Assuming that Fig. 7 is superimposed on Fig. 8, and that the planes A and B of each are the same, .and that the radius r is the same in both figures, we can then write the following four independent equations of the X and Y components of force of the masses, as

Ms cos(94+180)+M. cos 6i=M1 cos 01 Md sin(0+l80)+M. sin a.=M1 sin 01 Ma cos 0d+M. cos 0=Ma cos 0:

Ma sin fia+Ml sin 8:=M2 sin 9:

Thus, if M1, M2, 01 and 02 are known, we can solve. for Md Me, 64 and 0,; since we have four independent equations. Likewise, if we have Md, Ms, 6d and 0', we can solve for Mr, Ma, 01 and 02. So, with static-dynamic balancing, we obtain the same balancing as with the usual two plane balancing.

According to the principles of the present invention, when the rotor is running at a proper balancing speed as determined by a speed con apparatus, signal voltages which are proporti al to the amount of unbalance and having a 1 quency determined by the rotor speed, are ger ated in crystal pick-oils responsive to rela oscillation of the rotor spin axis. These sig voltages are fed into a mixer stage of an ampli and the phasing of the signal voltages is del mined by the position of the relay 48 which is erated at a predetermined frequency of appri mately of the order of five seconds, if a balanc indicated before the fifth second is up, the phat will be automatically reversed as determined a suitable timing relay, for example. This mi stage determines whether to remove static or namic unbalance by reversing the polarity of signal voltage of one pick-oil; that is, if

relay is in dynamic cutting position and dyna: unbalance is present, the polarity of the in signal voltages and output signal voltages wili such that the two cutters used will operate multaneously to remove material from the ro these cutters being located for mechanical c venience apart around the rotor, one be adjacent the top of the rotor and the other jacent the bottom of the rotor so that they on diametrically opposite sides of the rotor. the timing relay is still in dynamic position 1 only static unbalance is present, the voltage nals reaching the preamplifier will be of op site phase and therefore cancel each other I so that no operation of the cutters takes p1:

Before entering the mixer stage, both am; tude and phase shifters (both electronic and 1 chanical) are provided for the adjustment of relationship of the pick-off signals to each at before they are mixed. From the mixer stage, combined signals pass to suitable phase shift which make it possible to adjust the angle which the cutters remove metal from the rc in relation to the signal. Once the phase sh: ers are set, they need not be altered so long the same type of rotor is being tested.

A meter is provided in the pro-amplifierv to dicate amplitude of unbalance, and an oscil scope is employed to show phase relationship tween the mechanical unbalance and vibrat signal, the oscilloscope indicating whether vib: tion is due to unbalance, hearings, or otl sources. From the pre-amplifler thesignal g through a filter which is tuned to the frequei of the rotor speed and eliminates all signals l cept those caused by out-of-balance vibrati The output of the filter is passed to a power a plifler having automatic volume control to c( trol the amplitude of the cutting signal in on to eliminate re-bound in the cutters. The pov amplifier drives the cutters. The polarity of t of these cutters is reversed according to whet] the rotor is being-balanced dynamically or st: ically. The cutting agent used is emery 010 out in narrow strips and fed continuously p: the rotor so that unused emery is continuously position for cutting, maintaining a uniform c1 ting, rate. The emery cloth is forced into cont: with the rotor once each revolution,.by means a plunger attached to the voice coil of a dynan speaker which is driven by the power amplifl When the rotor has reached a predetermin state of balance, relay means is operated to 1 verse the rotor to effect stoppage thereof in short period of time. Granules of emery a shavings from the rotor are continuously clean therefrom by the combination of a vacuum a air Jets.

' of the transformer secondary windings.

circuit for determining the speed and direction oi operation of the rotor;

Fig. 6 is a wiring diagram illustrating the cir-' cuits and apparatus used for effecting the re moval of material from the rotor; and.

Figs. 7 and 8 are schematic views illustrating.

the principles of operation.

Similar characters of reference are'used in all of the above iigures to indicate corresponding parts. g

The referencenumeral I'designates a rotor to be balanced, the said rotor being illustrated as a gyrov rotor, but it is to be understood that any type of rotor or rotating means may be balanced by the apparatus and method of this invention.

The shaft 2 of rotor l is shown carried by bearings l and 3', from which the rotor may be removed at will in a manner similar to that disclosed in the above-mentioned patent. The rotor I is illustrated as electrically driven from threephase leads 4, this rotor being provided with a I rotor field winding 5 supplied from .the leads I.

A starting button is shown at I for operating the running and reversing switch I, a holding relay 8 being provided for holding the button 5 depressed and in rotor-o erating position until the I position of switch 'I is automatically reversed and the rotor has come to rest. The three-phase power supply leads 9 supply energy through a transformer Ill and through a speed control relay II to the running and'reversing switch I. The speed control relay II functions under the control of a speed signal derived from a speed control circuit it. of which this relay is a part, to connect the rotor either across the speed control voltage or 150 volts A. C. supply. for example, the latter voltage being used-for starting. in order that the rotor will reach balancing speed as rapidly as possible. and after balancing speed is approached. the speed signal supplied from speed control circuit I3 and derived from a photne ect ic cell It responsive to-the speed of the rotor I serves to control the relay Ii to connect t e rotor with the speed control voltage. such as 105 volts in series with the low impedance coils III of the saturation reactors 39.

The starting pushbutton 6 and associated parts are shown more in detail in Fig. 4. As will be seen pressed, the lever 8' carrying the same turns about fulcrum l5 to actuatethe running andreversing switch I to running position with conta t blades l thereof contacting the upper stationarv contacts shown. and completing circuits from the secondary oi transformer Ill through leads II. speed control relav II, leads I8, switch blades I6. leads I9. holding relay 8. to the rotor field 5 of the rotor I. thereby placing a high voltage upon this rotor held and effecting rapid acce eration of the rotor at the start. Note that t e leads I1 are connected with the'outer ends Actually the push button I may be electrically consurface of the rotor I. which end surface preferably has a dark area ill and a light area 2|. A light source I! is arranged to have a pencil beam projected against the end of the rotor I for refleotion to the photocell ll. Thus, the rotation' of the rotor I produces an A. C. substantially square wave output from cell I I, which is supplied to the control grid of amplifier tube 23. Tube 2| has a screen grid connectedwith a delay circuit comprising a neon tube 24 and a condenser-potentiometer network 25, 28. When the rotor I initially accelerates from zero speed, the neon tube 24 -i.'ails to conduct the low voltage applied thereacross at this time, owing to the fact that a definite interval of time is required to charge the condenser 25. This time interval will depend upon the capacity of condenser 25 and also upon the setting of the potentiometer 25. After a short period, however, sumcient for the rotor to obtain a fairly high speed, the voltage'across the potentiometer 28 will be sufiicient to provide conduction to the neon tube 24, thereby biasing the screen grid of tube 23 to cause conduction of the tube and hence to supply a speed voltage to the connected circuits. The square wave output or the photoelectric cell II has manyharmonics, and the delay circuit 25. 26 serves to prevent the harmonics from causing an undesired operation of the speed control relay until a desired high speedhas been attained.

The output of the tube 23 is supplied to an intermediate amplifier tube 21 and from thence to aphase-sensitive amplifier 28. which also functions as a rectifier in that it provides a D. C. speed voltage output. The intermediate amplifier tube 21 is also supplied to a phase shiftin circult 30. the output of which is fed through tube SI and transformer 32 in phase opposition to the grids of push-pull connected tubes 33, 33'. The phase shifting circuit til functions to shift the phase of the speed voltage through 180, depending upon the frequency of the speed voltage, which in turn, of course. is dependent upon the speed of rotation of the rotor I. Hence the voltage output otthe phase sensitive amplifier 28 will be a D. C. voltage which will have a polarity of one sense or the other, depending upon whether the rotor speed exceeds or drops below a desired predetermined value.

The output of the phase sensitive amplifier passes through a low pass filter 34 and through an amplifier stage 35 to the actuating coil I I of speed control relay II. Thecontacts of relay II are normally biased by spring 31 to the high speed running position. -The coil II is connected in series with high impedance coils .38 of saturable reactors, 39. The. saturable reactors comprise core members respectively associated with the high impedance coils 3B and with low impedance coils 40, which in turn are connected in the rotor field circuit by the operation of speed control relay II. The high impedance coils 38 are shown connected to receive the D. C. speed voltage.

These saturable reactors function automatically to maintain the rotor speed substantially constant and at predetermined balancing speed, once therelay II' is operated'to throwswitch blades of relay II to the upper positions shown in Fig. 4. In other words, if the rotor speed should increase, the speed voltage will be of such polarity as to cause the increased resistance to the flow of current to the rotor field windings, thereby causing deceleration; and if the rotor speed shoulddrop below such predetennined desired balancing speed, the reverse would occur.

The portion of the apparatus affecting the balancing of the rotor is shown in detail in Figs. 1 and 6, and comprises a pair of crystal pick-offs 42 and 42 which are connected with the bearings 3, 3'. The output of pick-off 42 is shown connected to the grids of amplifier tubes 43 and 44, where as the output of 42' is connected to the grid of amplifier tube 45. From the tubes 43,

44, and 45, these signals are passed to a phase shifting and mixer stage 48. .When testing for static unbalance, the output of crystal pick-01f 42 is connected to tube 43, which is then operating, whereas tube 44 is biased oil, as will further I appear.

When connected withtube 43, the output of pick-off 42 is connected in the same phase sense as the output of pick-oft 42' connected to tube 45, i. e., at this time the phase outputs of tubes 45 and 43 will be similar. For dynamic testing the output of pick-oil 42 is connected to tube 44, the output of which is in opposite phase sense to that of tube 45 receiving the signal from pickoil' 42'. The means for determining the sense of the output of pick-oil 42 constitutes the multivibrator 41 and the connected relay 48, the relay 48 being operated from multivibrator 41. The multivibrator 41 is further adjusted so that the relay 48 is operated at a predetermined frequency of approximately five seconds, so that it is in position five seconds for dynamic unbalance, then' five seconds for static unbalance, whereupon the cycle repeats.

When the signals are in opposite phase sense, i. e., when tubes 45 and 44 are amplifying signals, the pick-oil's are connected for a dynamic test through the action of multivibrator 41 and relay 48. I 'he two signals thus combined in the mixer 46 are supplied preferably through anamplifler 50 to a relay II, the output of which serves to control the operating coils n. 53 of solenoids 52'. and'fl'. Amplifier '50 preferably incorporates an automatic volume control. The switch arms of relay ii. are controlled by the output of multi-,- vibrator 54. which multivibrator is preferably synchronized in its operation with the multivibrator 41 by the synchronizing connection shown, whereby when undergoing a dynamic test, for example, the plunger of the solenoids I2, 53 will operate simultaneously, and when undergoing a static test, theseplungers will operate 180" out of phase.

Thus, when the signal voltages from the pickoiis are suppliedout of phase to the amplifier l0,

the output oi' the-amplifierawilfbe connected: through relay ii :to cause the ,plungers to press against the work simultaneously on opposite sides of the rotor to correct for dynamic unbalance. When the. signals are supplied inphase relation, th solenoids are connected through relay it to the output of amplifier l4 so-that theywill operate 180" out -of phase, or approach the work on the samejlside ottherotor. The solenoids '52 and II" press against' cuttingstrlps 56 and 55',

minals connecting the rotor to the transformer Ill, but with the polarity of one of the phases reversed so that the rotor l is rapidly stopped.

When the rotor ceases to rotate, the electronic controller releases the holding relay 8 and the balanced rotor is ready to be removed from the automatic balancing machine.

Since many changes could be made in the above construction and many apparently widely difi'erent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense. I

What is claimed is:

1. Automatic rotor balancing apparatus com-'- prising means for receiving and supporting a rotor, speed control means for automatically bringing the rotor up to a predetermined speed, electric pick-oil means for automaticallytesting the rotor for unbalance and for producing voltage signals responsive'to any unbalance, electric circuit means responsive to said voltage signals, and cutter members controlled. from said electronic circuit means for automatically removing metal from two spaced selected planes of the rotor to effect balancing the same.

2. In automatic rotor balancing apparatus for balancing rotors, means for receiving and supporting a rotor, means for bringing the rotor up to a desired predetermined speed, means for producing alternating electromotive forces responsive to unbalance of the rotor, means utilizing said electromotive forces to detect static and dynamic unbalance of the rotor, and cutting means positioned on opposite sides of the rotor and responsive to such unbalance for automatically removing material from the rotor to balance the same.

3. Apparatus of the character described for automatically testing rotors for unbalance, comprisingmeans for supporting a rotor to be tested, pick-off means for producing signal voltages proportional-to the amount of unbalance of the v rotor at a frequency determined by the rotor speed, means for receiving said signal voltages and for determining whether to remove static or dynamic unbalance by reversing the polarity of at least a portion of said voltages, and cutter means controlled from said last-named means amount of unbalance, said voltages having their which may be-ofemeryI-cloth; forfexample, and

which are continuously moved gradually past the ends of the solenoid plungersll'iand 44.

When the multivibrator's 41; have completed two cycles without indicating an error (out of balance) the error trigger clrcuit'operates the relay I, connectingthe contacts II to thelowerterfrequency determined by the rotor speed, an

amplifier and a connected mixer for receiving said signal voltages, relay means for phasing said voltages at a predetermined frequency whereby said mixerdetermines the-existence of static or dynamic unbalance, and servo means controlled from said mixer and comprising cutters operable simultaneously during dynamic testing to cut material from the rotor at opposite sides thereof to eflect. dynamic balance, said cutters being operable in out-.of-phase relation during static testing to remove material from the same side of therrotor for efiecting static balancing.

7 5. Automatic rotor balancing apparatus oomprising upper and lower bearings for receiving balance, amplifler means supplied from said pick- 011 means, relay means for connecting the outputs 01' certain of said amplifiers in similar phase relation and alternately in opposite phase relation for dynamic and static unbalance, mixer means for receiving outputs of said amplifiers and servo mechanism controlled from the output of said mixer means, said servo mechanism comprising means for automatically cutting material from the rotor to eliminate both static and dynamic unbalance thereof.

6. Automatic rotor balancing apparatus as delined in claim 5 wherein said cutter means comprises solenoids located on opposite sides or the rotor and having plungers for pressing the emery cloth'against upper and lower portions of the rotor, said plungers operating simultaneously during the dynamic unbalance and 180 in outof-phase relation to correct for static unbalance.

7. In automatic rotor balancing apparatus for balancing rotors, means for receiving and supporting a rotor, means i'orbringing the rotor up to a desired predetermined speed, means for producing alternating electromotive i'orces responsive to unbalance of the rotor, means utilizing said electromotive forces to detect'static and dynamic unbalance oi the rotor, said last-named means comprising amplifiers and relay means for connecting the outputs of certain of said ampliflers in like phase relation for dynamic unbalance and tor connecting the outputs otcertain of said amplifiers in unlike phase relation for static unbalance, and cutting means responsive to such unbalance for automatically removing material from the rotor to balance the same.

' HUGHES M. ZENOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,544,521 Sosa June 30, 1925 I 2,171,927 Fuchs Sept, 5, 1939 2,243,379 Johnson May'27, 1941 2,243,457 Esval et a1 May 27, 1941 2,322,561 Bevins June22, 1943 2,327,606 Saltz Aug. 24, 1943 2,327,607 Saltz Aug. 24, 1943 2,327,608 Saltz Aug 24, 1943 2,327,609 Saltz Aug. 24, 1943 2,331,733 Senger Oct, 12, 1943 2,346,975 Laboulais Apr. 18, 1944 Certificate of Correction Patent No. 2,474,883 I July 5, 1949 HUGHES M. ZEN OR It is hereby certified that error appears in the printed specification of the above n as follows:

numbered patent requiring correotio Column 8, line 23, for the word electric read electronic;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 16th day of May, A. D. 1950. 7

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction Patent No. 2,474,883 July 5, 1949 HUGHES M. ZEN OR It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 23, for the word electric read electronic;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice. Signed and sealed this 16th day of May, A. D. 1950. 7

THOMAS F. MURPHY,

Assistant Uommz'eaz'oner of Patents.

Certificate of Correction Patent No. 2,474,883 July 5, 1949 HUGHES M. ZEN OR It is hereby certified that error appears in the printed specification of the above numbered patent requiring c0 d of th th day rrection as follows: Column 8, line 23, for the word electric read electronic;

t should be read with this correction therein that the e case in the Patent Oflice. of May, A. D. 1950. Y

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

